module4 beee

Electrical Energy Systems Engineering

• Encompasses generation, transmission, distribution, and utilization of electrical energy.

• Different machines serve specific purposes at each stage:

  • Alternators: Generate alternating current (AC).

  • Transformers: Step up/down voltage levels for transmission and distribution.

  • Motors: Different types include DC motors, synchronous motors, stepper motors, and induction motors; used in various industrial and domestic applications.

6.1 DC Generator

6.1.1 Principle

• A DC generator is a dynamic machine converting mechanical energy to electrical energy.

• Operates based on Faraday's Law of electromagnetic induction.

• Generates dynamically induced emf with three basic requirements:

  1. A steady magnetic field.

  2. A conductor capable of carrying current.

  3. Conductor movement within the magnetic field.

• Illustration of operation:

  • Steady magnetic field from pole pieces (N & S).

  • Rotating coil (ABCD) in the magnetic field induces emf.

  • Commutator makes the bidirectional induced emf unidirectional.

6.1.2 Construction

• Components of a DC generator include:

  • Stator: Houses the yoke, the main field system, and brushes.

  • Rotor: Contains the armature and commutator.

• Key parts:

  1. Yoke/Frame: Protects inner components and forms part of the magnetic circuit.

  2. Field System: Includes magnetic field poles and windings, crucial for creating necessary magnetic flux.

  3. Brushes: Made of carbon or graphite, these connect the generator to external circuits and tap off generated electrical energy.

  4. Armature: Laminated drum with slots housing conductors, facilitating energy conversion.

  5. Commutator: Connects conductors to the armature, causing current direction alternation.

6.1.3 EMF Equation

• Variables:

  • P: Number of poles

  • Φ: Flux per pole (Webers)

  • Z: Total number of armature conductors

  • A: Parallel paths between armature terminals

  • N: Armature rotation speed (RPM)

• Formula for average induced emf in a conductor:

  • [ E_g = \frac{P \Phi N Z}{60A} ]

• This represents no-load emf across the armature terminals.

6.1.4 Types of DC Generator

• Classification based on field winding excitation:

  • Separately Excited: Powered from a separate DC source.

  • Self-Excited: Powered from electrical energy developed in the armature.

• Types of Self-Excited Generators:

  1. Shunt Generators

  2. Series Generators

  3. Compound Generators

6.1.5 Equivalent Circuits

• Separately Excited Generator: Field winding connected to a separate source.

• DC Shunt Generator: Shunt field across armature terminals.

• DC Series Generator: Series field connected with armature.

• Formulas relating current and voltage in these circuits:

  • Shunt: [ E_g = V + I_a R_a + V_b + V_{ar} ]

  • Series: [ E_g = V + I_a (R_a + R_{se}) ]

6.1.6 Characteristics

• Open Circuit Characteristics (OCC): Voltage plotted against field current under no-load.

• Important points:

  • Linear and non-linear regions indicate saturation points and initial non-load voltage.

  • Factors affecting voltage buildup include:

    1. Residual flux.

    2. Connection of shunt field coil.

    3. Field circuit resistance.

    4. Generator rotation speed.

6.1.7 Applications of DC Generators

• DC Shunt Generators:

  • Suitable for constant voltage applications (e.g., battery charging, electroplating).

  • Used in providing field excitation for AC generators.

• DC Series Generators:

  • Utilized in series arc lighting, incandescent lighting, and regenerative braking.

• Compound Generators:

  • Enable constant voltage supply through compounding methods.

6.2 DC Motor

6.2.1 Principle

• Operates on the principle that a current carrying conductor in a stationary magnetic field produces force, causing it to move.

6.2.2 Construction

• Parts similar to those of generators: yoke, field system, brushes, armature, and commutator.

6.2.3 Working

• Both armature and field windings connected to DC supply.

• Current in armature conductors produces torque, causing rotation.

• As the armature moves, back emf is induced, which opposes the applied voltage.

6.2.4 Types of DC Motors

• DC Shunt Motor: Voltage equation given in electrical circuit diagram.

• DC Series Motor: Series connection of windings affects operation.

6.2.5 Torque and Speed Equations

• Derived from mechanical principles and electrical equivalents.

• Power developed and torque equations can be calculated based on applied forces and motor design parameters.

6.2.6 Characteristics of DC Motors

• Important relationships characterized:

  • Torque vs. Armature Current.

  • Speed vs. Armature Current.

  • Speed vs. Armature Torque.

  • These characteristics align with different operational requirements for all motor types.